By default, when the user types a string into the ComboBox that matches one of its items, the item is selected and the text that the user typed is replaced. This can cause the text that the user entered to change case. If the ShouldPreserveUserEnteredPrefix property is set to true, the ComboBox selects the matching item, but preserves the text that the user entered. For example, suppose that a ComboBox contains the string, "Hello" (with a capital H) and the user enters "hello" (with a lowercase h). If ShouldPreserveUserEnteredPrefix is false, the ComboBox selects the matching item, "Hello," in its collection and populates its text box with that string. If ShouldPreserveUserEnteredPrefix is true, "Hello" is selected from the collection, but the text box says "hello."